      (* (nth (rotate-pi2 n_i) part)
         (/ (- (square (Math/sin phi_n_i))
 	      (square (Math/sin phi_0)))
-	   (square (Math/sin phi_n_i)))),
+	   (square (double (second n_i))))),
 
      (<= phi_0 phi_n_i (- Math/PI phi_0))
      0.0,

     (* (nth (rotate-pi2 n_i) part)
	(/ (- (square (Math/sin phi_0))
	      (square (Math/sin phi_n_i)))
	   (square (Math/sin phi_n_i)))))))

;; Overall Energy and Force


(defn- gravitative-force
  "Computes given part of gravitative force in layout on the
  inf-irreducible element n_i."
  [layout n_i part information]
  (let [upper-neighbours (:upper-neighbours-of-inf-irrs information),
	inf-irrs (:inf-irrs information),
